ADE75 datasheet(47/148 Pages) AD

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Preliminary Technical Data

ADE75xx/ADE71xx

Rev. PrE | Page 47 of 148

both bits are cleared or set, the current channel used for

measurement is selected automatically based on the Fault

detection.

Fault Indication

The ADE75xx/ADE71xx provides an indication of the part

going in or out of a fault condition. The new fault condition is

indicated by the FAULTSIGN flag (bit5) in the Interrupt Status

When FAULTSIGN bit (bit 6) of ACCMODE register (0x0F) is

cleared, the FAULTSIGN flag in the Interrupt Status Register 1

SFR (MIRQSTL, 0xDC) will be set when the part is entering

fault condition.

When FAULTSIGN bit (bit 6) of ACCMODE register (0x0F) is

set, the FAULTSIGN flag in the Interrupt Status Register 1 SFR

(MIRQSTL, 0xDC) will be set when the part is entering normal

condition.

When the FAULTSIGN bit is set in the Interrupt Enable

the Interrupt Status Register 1 SFR (MIRQSTL, 0xDC) is set, the

8052 core has a pending ADE interrupt.

Fault with Active Input Greater than Inactive

Input

If IA is the active current input (that is, being used for billing),

and the voltage signal on IB (inactive input) falls below 93.75%

of IA, and the FAULTSIGN bit (bit 6) of ACCMODE register

(0x0F) is cleared, the FAULTSIGN flag in the Interrupt Status

filtered and averaged to prevent false triggering of this logic

output. As a consequence of the filtering, there is a time delay of

approximately 3 s on the logic output after the fault event. The

FAULTSIGN flag is independent of any activity. Because IA is

the active input and it is still greater than IB, billing is

maintained on IA, that is, no swap to the IB input occurs. IA

remains the active input.

Fault with Inactive Input Greater than Active

Input

If the difference between IB, the inactive input, and IA, the active

input (that is, being used for billing), becomes greater than

6.25% of IB, and the FAULTSIGN bit (bit 6) of ACCMODE

Status Register 1 SFR (MIRQSTL, 0xDC) is set. The analog

input IB becomes the active input. Again, a time constant of

about 3 s is associated with this swap. IA does not swap back to

the active channel until IA is greater than IB and the difference

between IA and IB—in this order—becomes greater than 6.25%

of IB. However, if FAULTSIGN bit (bit 6) of ACCMODE

Status Register 1 SFR (MIRQSTL, 0xDC) will be set as soon as

IA is within 6.25% of IB. This threshold eliminates potential

chatter between IA and IB.

Calibration Concerns

Typically, when a meter is being calibrated, the voltage and

current circuits are separated as shown in Figure 23. This means

that current passes through only the phase or neutral circuit.

Figure 23 shows current being passed through the phase circuit.

This is the preferred option, because the ADE75xx/ADE71xx

starts billing on the input IA on power-up. The phase circuit CT

is connected to IA in the diagram. As the current sensors are not

perfectly matched, it is important to match current inputs. The

ADE75xx/ADE71xx provides a gain calibration register for IB,

IBGAIN (address 0x1C). IBGAIN is a 12-bit signed 2-

complement register that provides a gain resolution of

0.0244%/LSB.

For calibration, a first measurement should be done on IA by

setting SEL_I_CH bits to 0b01 in the CALMODE register

(0x3D). This measurement should be compared to the

measurement on IB. Measuring IB can be forced by setting

SEL_I_CH bits to 0b10 in the CALMODE register (0x3D). The

Gain error between these two measurements can be evaluated

using:

()

( )

()

Measuremen

Error

−

The two channels IA and IB can then be matched by writing: –

Error(%) / (1 + Error (%)) * 212 to IBGAIN register. This

matching adjustment will be valid for all energy measurements,

Active power, reactive power, Irms, and Apparent power, made

by the ADE75xx/ADE71xx.

AGND

TEST

CURRENT

240V RMS

Figure 23. Fault Conditions for Inactive Input Greater than Active Input

di/dt CURRENT SENSOR AND

DIGITAL INTEGRATOR14

A di/dt sensor detects changes in magnetic field caused by ac

current. Figure 24 shows the principle of a di/dt current sensor.

14 This function is not available in ADE7566 and ADE7166 products.

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